1. Field of the Invention
The present invention relates to a method and apparatus for laminating a film onto a semiconductor substrate and a manufacturing method of a semiconductor device using the film lamination method and, more particularly, to a method of laminating a die-attachment film, such as a die-attachment sheet material or a fixation film, onto a backside of a semiconductor substrate.
2. Description of the Related Art
In a manufacturing process of a semiconductor device such as a semiconductor integrated circuit (IC), circuit elements such as a transistor, a resistor, etc., and wiring layers for mutually connecting the circuit elements and further external connection electrodes are formed on one of the principal surfaces of a semiconductor substrate such as a silicon wafer so that a plurality of semiconductor element areas are formed on the one of the principal surfaces.
Thereafter, in a so-called post process, thinning of the substrate is performed by grinding another principal surface (backside) of the semiconductor substrate, and individualization of chips is performed by dividing (dicing) each of the semiconductor element areas, and further each semiconductor chip is subjected to encapsulation or accommodation into a container.
In such a post process, when encapsulating the semiconductor chip or accommodating the semiconductor chip into a container, a process is taken in which the semiconductor chip is firmly attached onto a lead frame or a support substrate such as a resin substrate or a ceramic substrate. Conventionally, a paste or a film for fixing the chip is previously applied onto a die stage of the lead frame or a chip mounting part of the support substrate, and, thereafter, the chip is mounted and fixed.
Accordingly, the mounting and fixing process of the semiconductor element is complicated and troublesome.
In order to attempt an increase in efficiency of the mounting/adhesion process of the semiconductor element, it is suggested to apply or laminate, prior to the dicing process of the semiconductor substrate, a die-attachment film (a die-attachment sheet material, a fixation film) onto the entire backside of the semiconductor substrate and, thereafter, the dicing process is performed.
According to the above-mentioned approach, an adhesive layer for adhesion is provided on the backside of each of the individualized semiconductor chips. Thus, the semiconductor chip can be easily mounted and fixed onto the die stage or the chip mounting part of the support substrate, which results in an increase in efficiency of the assembly process.
It should be noted that the die-attachment film is made of, for example, an epoxy resin as a main body, and generates an adhesion force by being heated.
In the lamination process of the die-attachment film onto the backside of the semiconductor substrate, as shown in FIG. 1, a die-attachment film 2 is laminated on the top surface of the semiconductor substrate 1 by pressing a rubber made pressing roller 3 against the die-attachment film 2 arranged on the top surface of the semiconductor substrate 1 while heating the entire surface of the semiconductor substrate 1 by a heater from the bottom surface of the semiconductor substrate 1 in the process of laminating the die-attachment film 2 after back-grinding the semiconductor substrate 1. That is, it is a method of heating a work (semiconductor substrate 1) by heating a table 4 on which the work is attached by embedding a heat generator (heater) in the table 4. Such a method is disclosed in Japanese Laid-Open Patent Application No. 2002-76096.
The above-mentioned method has no problem if the work has a sufficient strength. However, if the semiconductor substrate is thinned and the strength is reduced, there is a problem in that the semiconductor substrate cracks due to a thermal stress caused by a thermal expansion when the semiconductor substrate is entirely heated in the process of laminating the die-attachment film.
As measures for solving such a problem, a method is suggested in which the adhesion and fixation of the semiconductor surface onto the entire bottom surface of the semiconductor substrate 1 is not performed and, instead, the die-attachment film 2 is heated by a metal made pressing roller 3A in which a heat source or heat-generating part is incorporated as shown in FIG. 2. In this case, it is not necessary to incorporate a heat source into the table 4A.
Moreover, another method is suggested in which the die-attachment film 2 is laminated by heating while blowing a hot air onto the die-attachment film 2 or the semiconductor substrate 1 at a position immediately before the pressing roller 3 in a moving direction of the pressing roller 3.
Furthermore, Japanese Patent Publication NO. 7-25463 suggests a method in which a plurality of rollers having different widths are arranged so as to laminate the die-attachment film by consecutively pressing the rollers onto the die attachment film from one having a smaller width. This method is especially effective in laminating the die-attachment film while preventing air entering between the die-attachment film and a warped semiconductor substrate.
With the miniaturization and speeding up of electronic equipment, semiconductor devices to be incorporated in the electronic equipment are required for further miniaturization and high-density mounting. For this reason, there is a demand for thinning the semiconductor devices. However, it was difficult to laminate a die-attachment film on a thin semiconductor substrate by using the above-mentioned conventional method.
As mentioned above, if an entire surface of a semiconductor substrate is heated, the semiconductor substrate cracks due to a thermal stress. Thus, in order to avoid such a problem, it is effective to laminate a die-attachment film while partially heating the semiconductor substrate by a heat source incorporated in a pressing roller.
However, when incorporating a heat source into a pressing roller, the pressing roller must be formed of a material having a heat resistant temperature higher than a temperature required for the lamination. The die-attachment film presently used requires a heating temperature of about 180° C. The material of the pressing roller, when using such a film, is limited to a material such as metal or a material having a heat resistant temperature corresponding to metal.
Moreover, a high flatness is required for a surface of a roller, which is formed of a hard material such as metal. For example, when laminating a die-attachment film to a semiconductor substrate having a diameter of 200 mm, it is difficult to maintain a surface of a roller at a high flatness since a width of the roller must be 200 mm or more.
That is, if a film having a high temperature for lamination is used when a heat source is incorporated into a pressing roller used for the lamination (refer to FIG. 2), the pressing roller must be formed of a material having a heat resistance such as metal in consideration of the thermal conductivity of the pressing roller. In order to laminate without air and wrinkles over the entire surface of a substrate, a surface flatness of an order of micron is required for a metal made pressing roller and a semiconductor substrate. However, all the metal made roller, the semiconductor substrate and a chucking table onto which the semiconductor substrate is attached are considered as rigid members, and it is difficult to satisfy the requirement of high flatness required for lamination by merely increasing the surface flatness of each of the above-mentioned parts. Therefore, there may be a position at which the pressing roller partially contacts at one end in the range of a large semiconductor-substrate area. This partial contact of the pressing roller may be referred to as one-side contact. As a result, there is a problem in that air bubbles or wrinkles are formed in the laminated die-attachment film.
If the die-attachment film and the substrate are heated by blowing a hot air immediately before a roller (refer to FIG. 3), the above-mentioned problem associated with the surface flatness can be solved by forming the roller by a rubber material. In a case in which a high-temperature hot air is blown such as a condition for laminating a die-attachment film, there is no problem if the die-attachment film is thick. However, if the die-attachment film is thin, an elongation occurs in the part to which the hot air is blown, which results in a partially very thin film. In the worst case, there may happen a problem in which the die-attachment film is melted. Additionally, since a die-attachment film tends to be thinner in the future, it is expected that this problem becomes more remarkable.
There is another problem in the method of using a pressing roller formed of a rubber material. That is, there is a problem in that, depending on the surface condition of a pressing roller, a die-attachment film may adhere onto not a semiconductor substrate but the pressing roller. This problem is avoidable by applying a special process such as coating on the surface of the pressing roller so as to improve separability between the die-attachment film and the pressing roller. However, there is found no surface treatment which can be applied to a surface of a rubber made roller and also improve the separability.